The present invention is a method for purifying 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes. More specifically, the present invention is a method in which 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes contained in products or fractions consisting of 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes produced by a hydrosilation reaction of allyl methacrylate with dimethylhalosilanes or methyl dihalosilanes are decomposed, thus facilitating the fractional distillation of these compounds so that 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes can be purified to a high purity.
A method in which 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes are manufactured by subjecting allyl methacrylate and dimethylhalosilanes or methyldihalosilanes to a hydrosilation reaction and then subjecting the resulting products to a fractional distillation is known (see Polymer 26: 437, 1985). When these products are subjected to a fractional distillation a polymerization blocking agent is generally added in order to prevent gelation of the 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes. It is also known that 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes can be fractionated with a good yield by using metal halides such as tin chloride, antimony chloride, mercury chloride, copper chloride, bismuth chloride or cobalt chloride as polymerization blocking agents (see Japanese Patent Application Kokai No. 5-271248 and Japanese Patent Application Kokai No. 5-301881).
However, even using fractional distillation, it has not been possible to purify 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes to a high purity. In investigating the causes of this, the present inventors confirmed that products consisting of 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes produced by a hydrosilation reaction of allyl methacrylate with dimethylhalosilanes or methyl dihalosilanes, as well as fractions obtained by subjecting such products to fractional distillation, contain small amounts of 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes which are by-products of the hydrosilation reaction. The boiling points of these 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes are close to the boiling points of 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes so that it is difficult to separate these compounds; accordingly, the purity of the 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes drops. Such 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes contained in 3 -methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes sometimes create problems. For example, 1-methyl-2-methacryloxyethyldimethylchlorosilane produces impurities such as dimethyldichlorosilane by the following decomposition and interchange reactions:
Formula I ##STR1##
Specifically, the object of the present invention is to provide a method in which 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes contained in products or fractions consisting of 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes produced by a hydrosilation reaction of allyl methacrylate with dimethylhalosilanes or methyldihalosilanes are decomposed. Thus, facilitating the fractional distillation of these compounds so that 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes can be purified to a high purity.
In investigating metal halides as polymerization blocking agents for use in the abovementioned fractional distillation, the present inventors discovered that 1-methyl-2-methacryloxyethyldimethylhalosilanes or 1-methyl-2-methacryloxyethylmethyldihalosilanes contained in products consisting of 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyldihalosilanes are selectively decomposed, and that by thoroughly decomposing these silanes and then subjecting these compounds to a fractional distillation it is possible to purify 3-methacryloxypropyldimethylhalosilanes or 3-methacryloxypropylmethyl dihalosilanes to a high degree of purity. Furthermore, the inventors also discovered that copper (I) chloride and copper (II) chloride can be effectively used in order to perform the abovementioned decomposition reaction under relatively mild conditions, and that copper (I) chloride makes it possible to perform this decomposition reaction more quickly under mild conditions (i. e., at a low temperature) than copper (II) chloride.